(1) Field of the Invention
The present invention relates to high density fine ceramic sintered bodies useful for engine parts, gas turbine parts, mechanical parts, wear resistant slide members, and the like, and a process for manufacturing the same.
(2) Related Art Statement
In order to produce ceramic products, it is a conventional practice, as shown in a flow chart of FIG. 5 by way of an example, a ceramic raw material is first mixed with a sintering aid, and the mixture is ground and passed through a sieve of 44 .mu.m to remove foreign matters such as broken pieces of grinding media used for the grinding. Then, after granulating, water is added to the granulated powder as necessary, and the granulated powder is shaped by a mold press or a cold isostatic press. The shaped body is finally sintered at a given temperature to obtain a sintered product.
However, since a positive measure is not taken to uniformly disperse water in the granulated powder in the above-mentioned conventional ceramic product-producing process, an amount of water locally varies in the granulated powder. As a result, pores are formed in shaped bodies due to non-uniform particle fracture which is caused by non-uniform water distribution in the granulated powder, so that such pores remain in the sintered products. Consequently, ceramic sintered bodies having excellent mechanical characteristics cannot be obtained.
Particularly, when ceramic sintered bodies are used as bearing members, wear resistant members or slide members, pores and hardness largely influences the use life thereof. Thus, in order to obtain ceramic products having longer use life than before, it was necessary to produce high hardness ceramic sintered products having a smaller pore diameter and a smaller porosity. Among them, when they are used as bearing materials, it is known that it's important to grasp rolling fatigue life of the materials. Thus, there has been a demand to develop dense, high strength, and/or high hardness ceramic materials to improve rolling fatigue life.